Journal of Structural Engineering

The paper presents the experimental investigation of full-scale RC corner beam-column joints without transverse reinforcement in the joint region leading to nonductile behavior in many exiting RC buildings. The experimental study considered two design parameters: joint aspect ratio and beam longitudinal reinforcement ratio. Four corner beam-column joint specimens were constructed with transverse beams and floor slabs and tested under quasi-static cyclic loading. The specimens experienced joint shear failure without beam hinging mechanism as a result of the absence of transverse reinforcement in the joint region. On the basis of the test results, the paper discusses the effects of these two design parameters and the floor slab on the behavior of corner beam-column joints. The joint shear strengths obtained from the test specimens are compared with the strength recommendations of the ASCE/SEI 41-06 provisions.

A variety of connector details are used to provide integrity and force transfer between precast concrete panels in building floor diaphragms. To assess the adequacy of these connectors a large number of experiments have been conducted on discrete welded connectors used in precast concrete double-tee floor panels. A standard procedure for developing simplified response curves from original test data is used to generate simplified curves from each of the tests conducted. The calculated results of over 200 experiments are summarized in a comprehensive performance database. This database provides the stiffness, strength, and deformation properties of each connector detail examined. The connectors are divided into one of the following three displacement-based categories: low deformation element (LDE), moderate deformation element (MDE), and high deformation element (HDE), based on the performance measured in the experiments. A simplified pushover modeling approach is developed to estimate the in-plane maximum midspan flexural deflection and shear sliding of a diaphragm subjected to a static uniform load applied parallel to the span of the diaphragm system. This method begins with developing the shape functions of the joint moment-rotation and shear-sliding deformation responses by utilizing the information included in the performance database and then by estimating the in-plane flexural and shear resistance-displacement responses of the diaphragm system. Estimation of flexural and shear responses of the diaphragm designed with connectors in the LDE, MDE, and HDE categories are conducted as examples.

The paper describes a numerical model to analyze the fatigue behavior of RC anchorage zones. The model takes into account the cycle-dependent bond-slip behavior at the steel-concrete interface and is able to reproduce the experimental increase of the relative slip developed with number of load cycles, as well as the process of redistribution of stresses that takes place over the anchorage length as a result of fatigue damage. The results compare satisfactorily with existing experimental results. The model has been used to derive $S\text{-}N$ curves to provide the fatigue strength of anchorage zones under different confinement conditions and various values of the anchorage length-to-diameter ratio and the steel diameter. The results indicate that the confinement degree plays a significant role in the fatigue bond strength: no fatigue problems are found for the well-confined concrete condition, but significantly short fatigue strength is obtained under the moderately confined and unconfined concrete conditions.

The lifting of horizontally curved beams (or almost-straight beams with an imperfection in shape) is considered, with application in the construction of bridges. A circularly curved beam that is suspended at two symmetric locations by vertical or inclined cables is analyzed. The cross section of the beam is assumed to be doubly symmetric, the material is assumed to be linearly elastic, the cross-sectional dimensions are assumed to be small relative to the radius of curvature, and the deformations are assumed to be small. Both uniform (St. Venant) torsion and inclusion of nonuniform (warping) torsion are treated. Analytical equations are derived for the overall roll angle of the beam, the internal forces and moments, the weak-axis and strong-axis deflections, and the cross-sectional angle of twist. The behavior depends crucially on the locations of the lift points.

Dynamic response of composite beams with partial interaction is presented using a one-dimensional finite-element model based on a higher-order beam theory. The proposed model takes into account the effect of partial shear interaction between the adjacent layers, as well as the transverse shear deformation of the beam. A third order variation of the axial displacement of the fibers over the beam depth is taken to have a parabolic variation of shear stress, which vanishes at both the top and bottom fibers of the transverse composite surface, as clearly derived on the free and tangentially unloaded surface of the continua. In the proposed finite-element model, there is no need to incorporate any shear correction factor, and the model is free from the shear locking problem. The proposed numerical model is validated by comparing the results with those available in the literature. Many new results are presented, because there are no published results on vibration and buckling of composite beams based on higher-order beam theory.

External corrosion is found in many onshore oil and gas pipelines, and corrosion is a major cause of structural failure of these pipelines. Onshore buried pipelines can be subjected to axial, bending, shear, and other complex loadings as a result of geotechnical movements and temperature variations. In addition, these pipes experience internal pressure from the fluids that they transport. Pipeline industry is concerned about the structural behavior and integrity of corroded pipelines when subjected to various loads and load combinations. Hence, structural behavior and failure conditions of corroded pipelines under various loads and load combinations need to be understood for safe operation of these field pipelines. A literature review did not reveal any studies that determined the structural behavior of corroded steel pipes when subjected to monotonically increasing axial compressive force with constant internal pressure. Therefore, an experimental study was completed to determine the structural behavior of X46 steel line pipe subjected to monotonically increasing axial compression and constant internal pressure as the geometry of corrosion and level of internal pressure change. This study shows that the axial load-carrying capacity reduces as the corrosion depth increases. However, this pipe is highly ductile and does not pose any threat to the structural integrity of the pipe when subjected to monotonically increasing axial deformation and constant internal pressure.

Based on the current knowledge of steel moment connections, an empirical predictive three-parameter exponential model to depict the moment-rotation ($M–\theta$) relationship of bolted flush endplate beam-to-beam (BFEB) connections is presented in this paper. The exponential model has three control parameters. For deriving the parameters of the model in terms of the connection description, the results of a wide parametric finite-element (FE) study including 468 analyses of BFEB connections is used. For the parameters of the model such as the intercept constant moment and yielding rotation, a power equation that takes into account the key geometrical properties of the connection detail is proposed by means of regression analyses of three-dimensional (3D) FE method (FEM) results. The statistical analyses on the prediction of all model parameters for all 468 cases are presented. Also, the major parameters of the $M–\theta$ curve, such as the elastic stiffness and strain hardening stiffness are also expressed as a combination of the model parameters. The moment-rotation curves obtained by the model are compared with various published connection tests and the 3D FEM research. The model yields acceptable results and is in good agreement with actual connection behavior.

The structural behavior of circular hollow section (CHS) T-joints subjected to axial brace compression in fire conditions was investigated. Five full-scale tubular joints with different brace-to-chord diameter ratios were tested under elevated temperature. The tests were in isothermal heating conditions, where the specimens were heated to the desired temperatures and then subjected to static load to failure. The ultimate strength and failure modes of these joints were investigated. It was observed that both the reduction in material strength and changes in localized plastification area beneath the brace decreased the ultimate strength of the joints as temperature increased. Furthermore, local buckling and ovalisation of the chords were found to be more concentrated around the joint region at elevated temperature. To the authors’ best knowledge, these tests were among the first reported experimental investigations in the ultimate strength and failure mechanisms of tubular joints at elevated temperature. To investigate the joint behavior at high temperature in greater detail, FEM was used. The finite-element models were first validated by the test results. The development of failure mechanisms of CHS T-joints at elevated temperature was then traced with the numerical models. The models were also used to quantify the effect of elevated temperatures on three parameters that directly affect the ultimate strength of the T-joints. The three parameters are boundary condition, precompression in the chord, and chord thickness.

Tianjin Jinta Tower is the first high-rise building built with steel plate shear walls in China. The main lateral force resisting system is the composite core tube composed of steel plate shear walls and concrete-filled steel tubular columns. To investigate the seismic performance of this structural system and to provide design instructions, two specimens of 2-bay and 5-story steel plate shear walls were tested under low-cycle reverse loading. The unstiffened steel plates of the first specimen were connected to the boundary beam and column frame by high-strength bolts. The steel plates of the second specimen were connected to the boundary frame by welding, and the steel panels were stiffened by channels. Both specimens showed satisfactory energy dissipation mechanisms during the loading process. For the unstiffened specimen with bolted connections, the considerable postbuckling strength generated excellent ductility and energy dissipation performance, but a slip at the bolted connections and the buckling of steel panels decreased the stiffness in the serviceability condition. The stiffened and welded specimen showed higher stiffness in the elastic range and excellent energy dissipation capacity, but the cost of stiffeners would decrease the economy of the steel plate shear walls.

This paper presents an experimental study of two full-scale steel beam-column assemblies, each comprising three columns and two beams, to (1) define their response characteristics under a column-removal scenario, including the capacity of the beams and their connections to carry loads through catenary action, and (2) provide experimental data for validation of beam-to-column connection models for assessing the robustness of structural systems. The assemblies represent portions of the exterior moment-resisting frames of two 10-story steel-frame buildings. One test specimen had welded unreinforced flange, bolted web connections, and the other had reduced beam–section connections. When subjected to monotonically increasing vertical displacement of the unsupported center column, both specimens exhibited an initial elastic response dominated by flexure. With increased vertical displacement, the connections yielded, and axial tension developed in the beams. The axial tension in the beams increased until the connections failed under combined bending and axial stresses. The test results show that the rotational capacities of both connections under monotonic column displacement are about twice as large as those based on seismic-test data.

This paper presents a computational investigation of the response of steel beam-column assemblies with moment connections under monotonic loading conditions simulating a column removal scenario. Two beam-column assemblies are analyzed, which incorporate (1) welded unreinforced flange bolted web connections, and (2) reduced beam section connections. Detailed models of the assemblies are developed, which use highly refined solid and shell elements to represent nonlinear material behavior and fracture. Reduced models are also developed, which use a much smaller number of beam and spring elements and are intended for use in future studies to assess the vulnerability of complete structural systems to disproportionate collapse. The two modeling approaches are described, and computational results are compared with the results of the full-scale tests described in the companion paper. Good agreement is observed, demonstrating that both the detailed and reduced models are capable of capturing the predominant response characteristics and failure modes of the assemblies, including the development of tensile forces associated with catenary action and the ultimate failure of the moment connections under combined bending and axial stresses.

This paper presents key parameters that affect numerical modeling of steel frame structures for reliable collapse simulations. The collapse assessment is based on experimental data obtained from a full-scale shaking table collapse test of a 4-story steel moment frame and a blind numerical analysis contest that was organized in parallel with the collapse test. It is shown that (1) there is no clear advantage between three-dimensional (3D) and 2D analyses in the prediction of a sidesway collapse mechanism for buildings with a regular plan view as in the case of study; (2) the assumption of Rayleigh damping leads to better predictions of structural response compared with stiffness proportional damping; and (3) accurate prediction of collapse necessitates that $P\text{-}\Delta$ effects always be considered in the analysis. It is also proven that accurate simulation of steel component deterioration is a key factor for reliable prediction of collapse behavior. On the basis of a synthesis of experimental and analytical studies, a few collapse mitigation alternatives are investigated. In particular, the effects of the strong-column/weak-beam ratio and exposed base plates on the collapse capacity are assessed. It is notable that a combination of bending strength increase and delay of local buckling in first-story columns is most effective for the enhancement of seismic performance against collapse.

Torsional response for one-way or two-way asymmetric linear/nonlinear structural systems under uni- and bidirectional seismic excitations increases the maximum displacement demand on structural systems. In this study, we consider instantaneous load eccentricities caused by the motion of the center of mass. The eccentricities, which are time dependent, exist even for linear elastic two-way symmetric structures under seismic excitations, as the relative displacement between the center of mass and center of stiffness may not necessarily be negligible. The quantification of this second-order effect on structural response is not available in the literature. Equations are developed and some numerical results are obtained by incorporating this second-order effect for linear elastic structures under bidirectional excitations to quantify the importance of this phenomenon. The results obtained by considering more than 100 ground motion records suggest that, on average, an underestimation of seismic displacement demand can occur if this second-order effect is ignored, especially for two-way symmetrical systems. The degree of underestimation depends on the dynamic characteristics of the system and the record.

Three unconventional details for the plastic hinge regions of bridge columns subjected to seismic loads were developed, designed, and implemented in a large-scale, four-span RC bridge. Superelastic shape memory alloys (SMAs), engineered cementitious composites (ECCs), posttensioned columns, and elastomeric bearings were used in three different piers to improve the seismic performance of the bridge in terms of minimizing damage and reducing residual displacements. The bridge model was subjected to a series of biaxial earthquake excitations with increasing amplitudes. The experimental results showed that, besides being effective in reducing permanent displacement of the bridge, the high-performance materials and details substantially reduced the damage at plastic hinge regions and modified significantly other response parameters of the bents compared with conventional RC construction. Higher ductility was observed in the pier with the SMA/ECC combination, and larger load capacity was exhibited by the pier with elastomeric pads. While rotations at the plastic hinges with high-performance materials were significantly larger than those measured at plastic hinges made of conventional RC, the measured residual strains in the longitudinal reinforcement in the plastic hinges with innovative details were smaller than those observed in RC plastic hinges.

A steel plate shear wall (SPSW) with thin, unstiffened web plates is one type of seismic lateral force–resisting system that is gaining popularity. SPSWs are used in low to midrise building construction typically with two or more frames in each orthogonal direction to resist seismic loading combined with gravity framing. The SPSWs therefore control the lateral force response of the building and the building’s natural periods of vibration. For design of any seismic load–resisting system, an estimation of the building’s first-mode period is necessary to calculate seismic loads and estimate resulting frame drift. This paper presents a method for estimating the first three natural periods of a SPSW with nonuniform properties along its height, accounting for both shear and flexural deformations of the system. The proposed method approximates the SPSW frame as shear and flexural systems separately to determine corresponding frequencies and then combines these frequencies using Dunkerley’s equation. A comparison of periods estimated using the approximate method with those obtained from modal analysis of detailed finite-element models suggests that the proposed method is appropriate for estimating the first-mode period of SPSW frames. The proposed method could be valuable for refining the seismic design of these frames or for verifying the results of large, complex steel plate shear wall building models.

Timber-concrete composite beams are statically indeterminate structures where a concrete topping is connected via shear connectors to a timber beam. Because effects such as drying shrinkage of concrete, variations of timber moisture content, and environmental temperature cannot freely occur, self-equilibrated stresses (eigenstresses) and additional deflection are induced in the composite beam and may reduce the structural safety at ultimate and serviceability limit states, respectively. The paper presents a simplified design approach suitable for implementation in codes of practice to account for these effects, which are all transformed into uniformly distributed loads to be combined with gravity load. The moisture content variations to consider in design are tabled based on climatic region, size of the timber section, type of exposure, and protective coating. These variations may become significant particularly for the deflection of composite beams with narrow timber sections exposed to outdoor sheltered conditions. Environmental variations and drying shrinkage of concrete are quite influential on the design, particularly when this is governed by deflection control at a serviceability limit state. Composite beams with solid timber slabs and stiff connection, and composite beams with narrow timber section exposed to outdoor conditions were found to be particularly sensitive to these environmental effects.